Update...
I bough some black Transtint and used DNA. Turned and tuned the toneboards, then a 24 hour soak. What I learned is that Maple, soaked in alcohol for 24 hours (vacuum to -25, then 60PSI pressure) will swell about 20%, after drying it will only be about 10% bigger than original. This would not have been a problem if I had not already tuned them. Once tuned, it's pretty hard to do anymore turning or even surface sanding since it's an odd shape. I did manage to get 5 out of 7 back to a usable size. As for stain penetration, I found the surface and especially the end grain to to jet black, the rest is grey and some wood seems to have taken up very little stain. Now I have dark grey stoppers, but I sort of like the look since you can still see the grain. Pictures when I'm done with the finishing. I don't know if the swelling has affected the sound yet. I decide to do the fine tuning after they had been completely finished. Live and learn. I may do this again, but will soak rough turned stock, and finish it on the lathe before cutting the toneboard down.